This invention relates to electrical power distribution systems wherein electrical energy generated at one location is transmitted to another location as an electromagnetic wave. More specifically, this invention relates to antenna structure in which the operation of combining or summing the electrical energy supplied by a plurality of power sources and the operation of radiating substantially the total energy supplied by those power sources are both effected within and by a compact module that defines the antenna.
Various arrangements have been proposed for the transfer of electrical power from a first location at which electrical energy is readily generated to a second, substantially remote location that requires electrical power wherein the energy is transmitted as an electromagnetic wave that propagates between the first and second locations. For example, power generating and distribution systems have been proposed wherein solar cells convert solar radiation to a DC electrical signal that is used (either directly or after accumulation and storage within batteries or other such devices) to power electronic circuitry that generates and transmits the desired electromagnetic (RF) signal. In such a solar power system and a majority of the other systems which employ electromagnetic radiation as the means for electrical power transfer, one or more oscillator circuits are utilized to generate an electrical signal at the desired frequency of transmission; the signal power is greatly increased through the use of power amplifier circuits; and the resultant high power signal is coupled to and radiated by one or more antennas.
One problem associated with generating and transmitting electrical power in this manner results from the limited power handling capability of the power amplifier stages. In particular, and especially in those systems utillizing solid-state (i.e., semiconductor) circuitry, the electrical signal power that must be supplied to the transmitting antenna in order to establish an electromagnetic field of suitable intensity greatly exceeds the power handling capability of presently available power amplifiers. This situation exists even when the transmitting antenna is a large array of antenna elements since the power handling capability of each antenna element of such an array substantially exceeds the power handling capabilities of a semiconductor amplifier that is configured for highly efficient operation.
To avoid the potential limitation posed by limited power handling capabilities of the amplifier stage, most prior art systems employ a corporate feed arrangement in which the electrical signal power provided by the system oscillator is split or divided to supply input signals to a large number of power amplifiers. The amplified signals provided by the numerous power amplifier circuits are then coherently combined or summed within subsequent circuit stages or devices to provide a high power signal that is coupled to the transmitting antenna structure. This technique, although satisfactory in some situations, exhibits several significant disadvantages and drawbacks. Specifically, although the necessary corporate feed and signal combining apparatus can be realized with combinations of various devices such as hybrid networks and other types of power splitters and power dividers, the resulting system configuration is often relatively complex in topology or geometry; is relatively large and heavy; and, hence, is often costly. Of even greater importance, such an arrangement reduces sytem efficiency and can compromise other system performance characteristics. First, with respect to system efficiency, each device or network that must be added to the system to recombine the amplified signals causes loss of signal power due to impedance mismatch, conduction (I.sup.2 R) loss, loss within the dielectric material of various types of devices that may be employed and radiation loss from exposed or unshielded portions of such arrangements. With respect to various other sytem performance characteristics, the insertion phase variation between power amplifiers and between corporate power combining components often makes it extremely difficult or impossible to control the phase of the signals being combined to the degree desired or even necessary. This not only causes further degradaton of system efficiency because the signals are not in total coherence but can also deleteriously affect the directional characteristics of the antenna pattern, should significant undesirable phase shift occur relative to the signals supplied to various elements of a transmitting array.
The above-mentioned disadvantages and drawbacks of an electrical power distribution system that utilizes a plurality of amplifiers and the prior art corporate feed and power combining techniques become especially important and critical relative to one type of recently proposed solar-powered electrical transmission system. In particular, because electromagnetic energy passes through the earth's atmosphere and blanketing cloud cover with far less attenuation than does solar energy and because solar panels on the surface of the earth receive energy only during daylight hours, there has been substantial interest in establishing a synchronous satellite having a large array of solar panels and a large microwave antenna array for beaming the produced electromagnetic energy to earth. Obviously, the above-mentioned factors of reliability, cost, size and weight of the various system components play a major role in determining the practicality of such a system. Further, because of the relatively high power output of such a system and the narrow beam radiation pattern that is required, an antenna array occupying a relatively large area and having a very large number of elements is required. To provide ease of assembly and potential servicibility, it is generally desirable to construct such an array as a plurality of identical units or modules that are structurally and electrically interconnected.
Accordingly, it is an object of this invention to provide a transmitting antenna and power combining arrangement suitable for use in a power transmission system wherein a plurality of relatively high frequency signals are combined and transmitted as an electromagnetic wave.
It is another object of this invention to provide a unitary transmitting antenna-power combining arrangement that is relatively simple in topology and structure and can thus be manufactured at a relatively low cost.
It is yet another object of this invention to provide unitary transmitting antenna-power combining structure that exhibits relatively low power loss (i.e., high efficiency) while simultaneously being relatively small in size and light of weight.
It is still a further object of this invention to provide transmitting antenna-power combining apparatus of the above-described type that is suited for use in forming the power combining-transmitting array within the DC-RF conversion system of a synchronous satellite which transmits electrical power to the earth.
Still further, it is an object of this invention to provide unitary transmitting antenna-power combining structure of the above-described type which is structured in modular form to thereby allow ready assemblage of a large transmitting array.
Even further, it is an object of this invention to provide unitary transmitting antenna-power combining module wherein the signals which are combined are provided by a plurality of solid-state power amplifiers that are contained within the module and additional circuitry is provided to maintain proper phase relationship throughout the entire arrangement.